Vinyl polymerization of norbornene by bis(salicylaldiminate)copper(H)/methylalumoxane catalysts

Article abstract of DOI:10.1021/om060173i

The polymerization of norbornene in the presence of different bis(salicylaldiminate)copper(II) complexes and methylalumoxane has been investigated. In all cases a high molecular weight vinyl-type polymer was obtained. The presence of electron-withdrawing nitro groups on the chelate ligand markedly increased the activity of the catalyst. The influence on the catalytic performances and polymer characteristics as a function of reaction parameters, such as temperature, duration, and content of free trimethyl aluminum in the commercial MAO, was studied.

Full text of DOI:10.1021/om060173i

Organometallics 2006, 25, 3659-3664
3659
Vinyl Polymerization of Norbornene by
Bis(salicylaldiminate)copper(II)/Methylalumoxane Catalysts
Carlo Carlini,*,† Simone Giaiacopi,† Fabio Marchetti,† Calogero Pinzino,‡
Anna Maria Raspolli Galletti,† and Glauco Sbrana†
Dipartimento di Chimica e Chimica Industriale, UniVersity of Pisa, Via Risorgimento 35,
56126 Pisa, Italy, and Istituto per i Processi Chimico-Fisici (IPCF)-CNR,
Area delle Ricerca del CNR, Via G. Moruzzi 1, 56124 Pisa, Italy
ReceiVed February 22, 2006
The polymerization of norbornene in the presence of different bis(salicylaldiminate)copper(II) complexes
and methylalumoxane has been investigated. In all cases a high molecular weight vinyl-type polymer
was obtained. The presence of electron-withdrawing nitro groups on the chelate ligand markedly increased
the activity of the catalyst. The influence on the catalytic performances and polymer characteristics as a
function of reaction parameters, such as temperature, duration, and content of free trimethyl aluminum
in the commercial MAO, was studied.
Scheme 1
Introduction
It is well established that bicyclo[2.2.1]hept-2-ene, better
known as norbornene (NB), can be polymerized by different
routes, affording polymeric products that are very different in
structure and properties (Scheme 1).1,2
Ring-opening metathesis polymerization (ROMP) is by far
the most investigated route, giving rise to a polyalkenamer that
still contains double bonds in the polymer backbone.3,4
On the contrary, both the cationic and radical polymerizations
give rise to a low molecular weight polymer with a 2,7-
connectivity of the monomeric units.5 Finally, it is also possible
to polymerize NB maintaining the bicyclic structure, i.e., only
opening the double bond, in a typical vinyl polymerization.1,6
This type of poly(norbornene) (PNB) is a special polymer, due
to its good mechanical properties, heat resistivity, transparency,
high glass transition temperature, and good solubility in polar
organic solvents. PNB has been deeply investigated for many
optical and microelectronic applications, and its films have
excellent optical transparency, heat stability, and good UV
resistance; therefore they can be employed as components for
condensers or cover layers for liquid-crystal displays.7-9
Moreover, the high optical transparency in the infrared region
of the spectrum makes PNBs very promising materials for data
storage and telecommunication waveguides.10
Up to now, catalytic systems based on titanium,11 zirconium,12
hafnium,13 vanadium,14 cobalt,15 chromium,16,17 nickel,17-20 and
palladium21-23 have been mainly reported for the vinyl polym-
erization of NB. Recently, rare-earth metals were also used in
such a reaction, although with a low activity.24
Notwithstanding that many efforts in the past five years have
been devoted to late-transition polymerization catalysts,25,26 no
(9) Varanasi, P. R.; Mewherter, A. M.; Lawson, M. C.; Jordhamo, G.;
Allen, R.; Opitz, J.; Ito, H.; Wallow, T.; Hofer, D. J. Photopolym. Sci.
Technol. 1999, 12, 493.
(10) Glukh, K.; Lipian, J.-H.; Mimna, R.; Neal, P. S.; Ravikiran, R.;
Rhodes, L. F.; Shick, R. A.; Zhao, X.-M. Proc. SPIE-Int. Soc. Opt. Eng.
2000, 4106, 43.
* To whom correspondence should be addressed. Fax: +39 050 2219260.
E-mail: carlini@dcci.unipi.it.
† University of Pisa.
‡ IPCF-CNR.
(1) Janiak, C.; Lassahn, P. G. J. Mol. Catal. A: Chem. 2001, 166, 193,
and references therein.
(11) Tritto, I.; Boggioni, L.; Sacchi, M. C.; Locatelli, P. J. Mol. Catal.
A: Chem. 1998, 133, 139.
(12) Kaminsky, W.; Bark, A.; Arndt, M. Makromol. Chem., Macromol.
Symp. 1991, 47, 83.
(13) Brekner, M. J.; Decker, H.; Osan, F. (Hoechst AG) EP Patent
683,797, 1994.
(14) Minchak, R. J.; Ware, J. T. (Goodrich, B. F) EP Patent 291,970,
1988.
(15) Goodall, B. L.; McIntosh, L. H., III; Rhodes, L. F. Makromol. Chem.,
Macromol. Symp. 1995, 89, 421.
(16) Peuckert, U.; Heitz, W. Macromol. Rapid Commun. 1998, 19, 159.
(17) Lassahn, P.-G.; Lozan, V.; Timco, G. A.; Christian, P.; Janiak, C.;
Winpenny, E. P. J. Catal. 2004, 222, 261.
(18) Barnes, D. A.; Benedikt, G. M.; Goodall, B. L.; Huang, S. S.;
Kalamarides, H. A.; Lenhard, S.; McIntosh, L. H., III; Selvy, K. T.; Shick,
R. A.; Rhodes, L. F. Macromolecules 2003, 36, 2623.
(19) Lozan, V.; Lassahn, P.-G.; Zhang, C.; Wu, B.; Janiak, C.; Rheinwald,
G.; Lang, H. Z. Naturforsch. B 2003, 58, 1152.
(2) Goodall, B. L. In Late Transition Metal Polymerization Catalysis;
Rieger, B., Baugh, L. S., Kacker, S., Striegler, S., Eds.; Wiley/VCH:
Weinheim, 2003; p 101, and references therein.
(3) Ivin, K. J.; Mol, J. C. Olefin Metathesis and Metathesis Polymeri-
zation; Academic Press: San Diego, 1997; p 407.
(4) Schwab, P.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc. 1996,
118, 100.
(5) Gaylord, N. G.; Deshpande, A. B.; Mandal, B. M.; Martan, M. J.
Macromol. Sci. Chem. 1977, A11, 1053.
(6) Makovetsky, K. L.; Gorbacheva, L. I.; Golenko, T. G.; Ostrovskaya,
I. Ya.; Bondarenko, G. N. NATO AdV. Study Inst. Ser., Ser. C 1998, 506,
69.
(7) Grove, N R.; Kohl, P. A.; Bidstrup-Allen, S. A.; Jayaraman, S.; Shick
R. A. J. Polym. Sci., Part B: Polym. Phys. 1999, 37, 303.
(8) Ahmed, S.; Bidstrup-Allen, S. A.; Kohl, P. A.; Ludovice, P. J. J.
Phys. Chem. B 1998, 102, 9783.
10.1021/om060173i CCC: $33.50 © 2006 American Chemical Society
Publication on Web 06/13/2006

3660 Organometallics, Vol. 25, No. 15, 2006
Carlini et al.
Chart 1
data have been reported, to the best of our knowledge, on the
copper-catalyzed NB vinyl polymerization.27 However, with the
exclusion of the atom transfer radical polymerization (ATRP)
systems,28,29 catalysts based on copper are in general rare and
deal with ethylene and acrylate homo- and co-polymeriza-
tion.25,30
Therefore, in the present article the vinyl polymerization of
NB catalyzed by different Cu(II) bis(salicylaldiminate) com-
plexes (I-V) (Chart 1) in combination with MAO will be
studied. In fact, these inexpensive, air-stable, and very easy to
synthesize copper precursors appear good candidates for this
type of reaction.
bis(salicylaldiminate)Cu(II) complexes the steric hindrance and
the electronic characteristics of the substituents on both the
phenol and the imine moieties influence the distortion from
planarity.32-34 However, for many of these substituted com-
plexes, X-ray structural data are not available and the above
stereochemical statements are based on spectroscopic studies.
In the case of the complexes I-V, due to their low solubility,
only IV was obtained in the crystalline state, and its structure
was determined by X-ray diffraction, as shown in Figure 1. The
geometrical parameters of the bonding around copper are listed
in Table 1. The crystallographic data together with the collection
parameters and the refinement parameters are summarized in
Table 2. IV may be described as distorted square planar. The
N and O atoms bonded to the copper are displaced by nearly
0.45 Å over and below the coordination mean plane, respec-
tively. A very similar coordination geometry has been reported
for Cu(II) complexes with 2-(2-oxy-5-bromo-3-nitrophenyl)-
4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl35 and 2-(3-
nitro-2-oxyphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-
1-oxyl36 ligands, which share with our ligand the encumbering
substitution on the iminic nitrogen and the nitro group in ortho-
position with respect to the oxygen. A similar structure was
also reported for bis(3,5-dibromo-N-o-tolylsalicylaldiminate)-
copper(II).37
In particular, the influence of the reaction conditions on their
catalytic behavior will be examined and the resulting PNBs will
be structurally characterized.
Results and Discussion
It is well known that four-coordinated Cu(II) complexes are
usually characterized by a square planar coordination that may
be distorted to pseudo-tetrahedral geometry.31 In particular, for
(20) Wang, H.-Y.; Jin, G.-X. Eur. J. Inorg. Chem. 2005, 1665.
(21) Mehler, C.; Risse, W. Macromolecules 1992, 25, 4226.
(22) Lassahn, P.-G.; Lozan, V.; Janiak, C. Dalton Trans. 2003, 927.
(23) Berchtold, B.; Lozan, V.; Lassahn, P.-G.; Janiak, C. J. Polym. Sci.
A: Polym. Chem. 2002, 40, 3604.
(24) Karl, M.; Seybert, G.; Massa, W.; Harms, K.; Agarwal, S.; Maleika,
R.; Stelter, W.; Greiner, A.; Heitz, W.; Neumuller, B.; Dehnicke, K. Z.
Anorg. Allg. Chem. 1999, 625, 1301.
Preliminary experiments on NB polymerization were carried
out in the presence of I as copper(II) precursor, characterized
by the presence of two electron-withdrawing nitro groups on
the salicylaldiminate ligand and of bulky isopropyl substituents
on the N-aryl moiety. Indeed, the corresponding nickel(II)
(25) Gibson, V. C.; Spitzmesser, S. K. Chem. ReV. 2003, 103, 283, and
references therein.
(26) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. ReV. 2000, 100,
1169, and references therein.
(32) Maslen, H. S.; Waters, T. N. Coord. Chem. ReV. 1975, 17, 137.
(33) Ferna´ndez-G, J. M.; Lo´pez-Durn, F. A.; Herna´ndez-Ortega, S.;
Go´mez-Vidales, V.; Macias-Ruvalcaba, N.; Aguilar-Martinez, M. J. Mol.
Struct. 2002, 612, 69.
(34) Garnovskii, A. D.; Nivorozhkin, A. L.; Minkin, V. I. Coord. Chem.
ReV. 1993, 126, 1.
(35) Tretyakov, E. V.; Eltsov, I. V.; Fokin, S. V.; Shvedenkov, Y. G.;
Romanenko, G. V.; Ovcharenko V. I. Polyhedron 2003, 22, 2499.
(36) Petrov, P. A.; Tret’yakov, E. V.; Romanenko, G. V.; Ovcharenko,
V. I.; Sagdeev R. Z. IzV. Akad. Nauk SSSR, Ser. Khim. (Russ.) (Russ. Chem.
Bull.) 2004, 53, 109.
(27) After the submission of this article the use of copper catalysts in
the presence of MAO as cocatalysts for NB polymerization was reported
(Lu¨, X.-Q.; Bao, F.; Kang, B.-S.; Wu, Q.; Liu, H.-Q.; Zhu, F.-M. J.
Organomet. Chem. 2006, 691, 821). Productivities up to 60 kg of NB/mol
Cu × h were reached, appreciably lower with respect to ours.
(28) Liu, S.; Elyashiv, S.; Sen, A. J. Am. Chem. Soc. 2001, 123, 12738.
(29) Xia, J.; Matyjaszewski, K. Macromolecules 1997, 30, 7697.
(30) Stibrany, R. T.; Schulz, D. N.; Kacker, S.; Patil, A. O.; Baugh, L.S.;
Rucker, S. P.; Zushma, S.; Berluche, E.; Sissano, J. A. Macromolecules
2003, 36, 8584.
(31) Knock, R.; Wilk, A.; Wannowius, K. J.; Reinen, D.; Elias, H. Inorg.
Chem. 1990, 29, 3799.
(37) Manriquez, V.; Costamagna, J.; Vargas, J.; Von Schnerir, H. G.;
Peters, K.; Acta Crystallogr. Sect. C 1990, C46, 1823.

Vinyl Polymerization of Norbornene by Copper(II) Catalysts
Organometallics, Vol. 25, No. 15, 2006 3661
Table 3. Homopolymerization of NB by the I/MAO
Catalytic System in Chlorobenzene Solutiona
Al/Cub
Al/Cuc
Td
time
(h)
f
run (mol/mol) (mol/mol) (°C)
Pe
Mw
PDIf,g
1
2
3
4
100
1000
2500
2500
2500
2500
375
2125
2500
1000
25
25
25
60
80
80
80
80
100
80
80
1
1
1
1
1
24
1
1
24
1
1
traces n.d.
n.d.
2.4
2.6
4.7
60
606 000
432 000
494 000
5
150
12
6
7h
8i
9
10
386 000
3.9
10
11
2500
a I: 1 µmol; NB/Cu: 10 000 mol/mol; chlorobenzene (total volume):
20 mL; n.d. ) not determined. b Al represents the total amount of aluminum
including the free TMA present in MAO-A. c Al represents the total amount
of aluminum including the free TMA present in MAO-W. d Reaction
temperature. e Productivity expressed as kg of PNB/mol Cu × h. f Deter-
mined by SEC analysis. g Polydispersity index, determined as Mw/Mn.
h TMA alone was employed; the Al/Cu molar ratio corresponds to that
present in MAO-A when an Al/Cu molar ratio equal to 2500 was used
(run 5). i TMA-depleted MAO was used (see Experimental Section). The
Al/Cu molar ratio equal to 2125 corresponds to that of 2500 in run 5, after
elimination of TMA in MAO-A.
polar solvent, where PNB is soluble, improves the catalytic
performances in NB vinyl polymerization.1
No catalytic activity was observed when I was adopted in
the absence of an organometallic cocatalyst. When 1 µmol of I
was employed at room temperature in combination with MAO-A
(containing about 15 mol % of free TMA and 85 mol % of
oligomeric MAO), no catalytic activity was ascertained up to
an Al/Cu molar ratio of 2500 (runs 1-3, Table 3), and also in
this case only traces of PNB were formed. When the reaction
temperature was increased to 60 °C (run 4, Table 3), a higher
productivity was observed to give a PNB sample with high mo-
lecular weight (Mw ) 606 000) and a polydispersity around 2.
No traces of oligomeric products were detected in the reaction
mixture. A further increase of the reaction temperature to 80
°C (run 5, Table 3) caused a further enhancement of the produc-
tivity up to 150 kg of PNB/mol Cu × h. When the reaction
time was prolonged to 24 h (run 6, Table 3), a modest increase
of the molecular weight was observed with a significant en-
hancement of its polydispersity. Taking into account that the
employed MAO-A contains about 15 mol % of free TMA, to
understand the role of this last component, run 5 was re-
peated in the presence of TMA alone, adopting an Al/Cu )
375 mol/mol (run 7, Table 3), corresponding to the content of
TMA introduced with MAO-A. No catalytic activity was
observed, and over-reduction of I with metal deposition was
also found. An analogous experiment carried out with I and
TMA-free MAO (Al/Cu ) 2125 mol/mol) (run 8, Table 3) again
did not show any catalytic activity. However, no metal deposi-
tion was observed in this case. These results clearly indicate
that both TMA and MAO are necessary for the activation of
the catalytic system. Similar results were obtained for ethylene
polymerization when bis(salicylaldiminate)nickel(II)/MAO cata-
lysts were employed.39
Figure 1. Two views of the molecular structure of IV in the 2-fold
axis direction (A) and normal to the 2-fold axis (B). The distorted
square planar coordination of the copper is evident from B. ′ )
-x, y, 1/2 - z. Thermal ellipsoids are at 30% probability.
Table 1. Selected Bond Distances (Å) and Angles (deg)
for IV
Cu-O(3)
N(2)-Cu-O(3)
N(2)-Cu-N(2′)
1.890(5)
92.5(2)
148.8(4)
Cu-N(2)
1.976(5)
93.9(2)
156.3(3)
N(2)-Cu-O(3′)a
O(3)-Cu-O(3′)
a The slanted prime in the label has the same meaning as in Figure 1.
Table 2. Crystal Data and Structure Refinement for IV
empirical formula
fw
C38H42CuN4O6
714.30
cryst syst
space group
a/Å
b/Å
c/Å
monoclinic
C2/c (No. 15)
14.624(4)
11.550(3)
21.827(4)
108.15(2)
3503.3(15)
4
1.354
0.676
4297
3457 [0.1164]
226
â/deg
U/Å3
Z
D
calc/Mg‚m-3
µ/mm-1
no. of measd reflns
no. of unique reflns [Rint
no. of params
]
R1, wR2 [I > 2σ(I)]
0.0946, 0.1613
1.000
goodness of fit on F2
When the reaction temperature was raised to 100 °C, a slight
decrease of the catalytic activity was observed (compare run 9
with run 6), thus suggesting that 80 °C is the optimum working
temperature.
complex was recently ascertained to be very active in NB
polymerization, when activated by a large excess of MAO as
cocatalyst (Al/Ni: 1000-2000 mol/mol).38 This catalytic be-
havior has been related to the presence of the nitro groups on
the phenol moiety.
(38) Carlini, C.; Martinelli, M.; Raspolli Galletti, A. M.; Sbrana, G. J.
Polym. Sci., Part A: Polym. Chem. 2006, 44, 1514.
(39) Carlini, C.; De Luise V.; Grillo Fernandes, E.; Martinelli, M.;
Raspolli Galletti, A. M.; Sbrana, G. Macromol. Rapid Commun. 2005, 26,
808, and references therein.
Chlorobenzene was chosen as a reaction medium for NB
polymerization experiments because it is well known that this

3662 Organometallics, Vol. 25, No. 15, 2006
Table 4. Homopolymerization of NB by II-V/MAO Catalytic Systems in Chlorobenzene Solutiona
Carlini et al.
Cu
precursor
Al/Cub
(mol/mol)
Al/Cuc
(mol/mol)
Td
(°C)
time
(h)
f
run
Pe
Mw
PDIf,g
12
13
14
15
16
17
18
19
20
21
22h
23h
II
II
II
II
III
III
IV
IV
2500
2500
2500
60
80
80
80
80
80
80
80
80
80
80
80
1
1
24
1
1
24
1
24
1
24
1
traces
110
11
traces
60
5
70
4
30
5
n.d.
n.d.
2.2
2.3
n.d.
2.9
3.1
2.4
3.1
3.2
3.3
344 000
411 000
n.d.
116 000
125 000
227 000
450 000
129 000
180 000
2500
2500
2500
2500
2500
2500
2500
2500
2500
V
V
Cu(OAc)2
Cu(acac)2
0
0
1
a Cu precursor: 1 µmol; NB/Cu: 10 000 mol/mol; chlorobenzene (total volume): 20 mL; n.d. ) not determined. b Al represents the total amount of
aluminum including the free TMA present in MAO-A. c Al represents the total amount of aluminum including the free TMA present in MAO-W. d Reaction
temperature. e Productivity expressed as kg of PNB/mol Cu × h. f Determined by SEC analysis. g Polydispersity index, determined as Mw/Mn. h Metal deposition
was observed.
When run 5 was replicated in the presence of a lower amount
of MAO-A (Al/Cu ) 1000, run 10), only traces of PNB were
formed.
tested (run 23, Table 4); also in this case under the adopted
reaction conditions over-reduction to metal was detected, never
ascertained in the case of the corresponding catalytic experi-
ments performed with precursors I-V.
With the aim of verifying the effect on catalytic activity when
different relative amounts of TMA and oligomeric MAO were
employed, run 5 was repeated by using MAO-W (containing
about 28 mol % of TMA), and hence the TMA concentration
almost doubled (run 11, Table 3). The complete deactivation
of the catalytic system was observed, an analogous detrimental
effect being previously observed with the corresponding nickel-
based catalysts.40
FT-IR and 1H and 13C NMR spectra of all the PNB samples
are typical of a nonstereoregular vinyl-type structure. In fact,
in the FT-IR spectra no signals related to double bonds were
1
observed in the 1680-1620 cm-1 region.18,41 Moreover, H
NMR analysis showed signals in the 0.9-2.6 ppm range,
whereas no resonances were observed in the 5-6.5 ppm region,
typical of vinylic hydrogen atoms.42
13C NMR spectra confirmed the above statements. In fact,
they showed the resonances of methylenes and methines at
29.5-33.5 ppm for C5 and C6 (see Scheme 1), at 35.5 and
38.5 ppm for C7, at 38.5-42.5 ppm for C1 and C4, and in the
46.6-54 ppm region for C2 and C3, according to what was
previously reported for vinyl-type addition PNBs.40,43
TGA analysis showed that all the PNB samples were stable
up to 450 °C. Our attempts to determine the glass transition
temperature (Tg) of PNB samples failed, DSC spectra not
evidencing well-defined endothermic signals upon heating to
the decomposition temperature, as previously observed for vinyl-
type PNBs obtained with other catalytic systems.18,44
When I was replaced by II, not containing the bulky isopropyl
groups on the N-aryl moiety but still bearing the nitro groups
on the phenol moiety of the ligand, once again no appreciable
catalytic activity was observed at 60 °C (run 12, Table 4).
When the temperature was raised to 80 °C (runs 13-15),
the catalytic performances, in terms of productivity and PNB
characteristics, were substantially similar to those observed in
the corresponding experiments carried out in the presence of
I. These results suggest that for these bis(salicylaldiminate)
Cu(II)/MAO systems the catalytic behavior is not significantly
affected by the presence or absence of bulky substituents on
the N-aryl moiety.
On the contrary, when III, not bearing nitro groups on the
phenol moiety, was employed in the place of I, a significant
reduction of both the catalytic activity and the molecular weight
was observed (runs 16, 17, Table 4). On the other hand, an
intermediate result was achieved when IV, containing only one
nitro group in the ortho-position of the phenol moiety, was
employed (runs 18, 19, Table 4), thus suggesting that the
presence of the electron-withdrawing nitro groups on the above
copper precursors plays an important role in the activation of
the catalysts.
Finally, when V, characterized by the presence of an N-alkyl
moiety, was employed as copper precursor, a further reduction
of the activity was observed (runs 20, 21, Table 4). In all cases
when the reaction time was prolonged to 24 h, a broadening of
the molecular weight polydispersity was observed, probably
related to the increase of the number of different active species.
To verify if commercial Cu(II) precursors in the presence of
MAO can be employed for NB polymerization, run 5 was
replicated employing Cu(II) acetate as precursor (run 22, Table
4). No catalytic activity was observed, and at the end of the
experiment metal deposition was ascertained. A complete
deactivation was also observed when Cu(II) acetylacetonate was
The observed vinyl-type structure of the resulting PNB
samples represents an indirect indication that a nonradical
reaction mechanism is working with the above copper(II)/MAO
catalytic systems. However, to gain a better insight into the
oxidation state of the active species, ESR studies were carried
out on the I/MAO-A catalytic system. The initial strong ESR
signal (Figure 2A) of the copper(II) precursor I at 293 K (giso
) 2.108, Aiso ) 78.6 G) was progressively reduced by the
addition of MAO-A, a complete disappearance of the Cu(II)
ESR signal (Figure 1C) being observed for an Al/Cu molar ratio
equal to 150. Moreover, no appearance of any other radical
species was ascertained, at least up to an Al/Cu molar ratio equal
to 2500. Taking into account that NB itself, due to its high
concentration, may behave as a stabilizing agent for the active
species, the above-described ESR experiments were repeated
in the presence of NB (NB/Cu ) 10 000 mol/mol). No
(41) Wu, Q.; Lu, Y. J. Polym. Sci. Part A: Polym. Chem. 2002, 40,
1421.
(42) Sato, Y.; Nakayama, Y.; Yasuda, H. J. Organomet. Chem. 2004,
689, 744.
(43) Nelkenbaum, E.; Kapon, M.; Eisen, M. S. Organometallics 2005,
24, 2645.
(44) Gao, H.; Zhang, J.; Chen, Y.; Zhu, F.; Wu, Q. J. Mol. Catal. A:
Chem. 2005, 240, 178.
(40) Borkar, S.; Saxema, P. K. Polym. Bull. 2000, 44, 167.

Vinyl Polymerization of Norbornene by Copper(II) Catalysts
Organometallics, Vol. 25, No. 15, 2006 3663
Figure 2. X-band ESR spectra at T ) 293 K of the catalytic system I/MAO-A (A, copper(II) precursor alone; B, Al/Cu molar ratio equal
to 15; C, Al/Cu molar ratio equal to 150).
significant spectral changes were observed, thus assigning the
stabilizing role to the oligomeric MAO alone.
Experimental Section
Materials. Manipulations of sensitive materials were carried out
under a dry argon atmosphere using Schlenk techniques. Chlo-
robenzene (Aldrich) and methylene chloride were refluxed on CaH2
for 8 h, distilled, and stored under dry argon. Methanol (Aldrich)
was dried by distillation under dry argon after refluxing for 6 h on
magnesium methoxide according to the Lund and Bjerrum method.47
Methylalumoxane was purchased from Witco as a 5 wt % solution
in toluene (free TMA content equal to 28 mol %) (MAO-W) and
from Azko Nobel as a 7 wt % in toluene solution (free TMA content
equal to 15 mol %) (MAO-A). Both were used as received and
stored in the refrigerator. TMA-depleted MAO was obtained from
MAO-A as a solid residue by high-vacuum distillation as previously
reported.46,48TMA (Aldrich) was used as received and stored under
dry argon. Norbornene (NB) (Aldrich) was refluxed for 2 h on Na,
distilled, and stored under dry argon. NB was employed as a 20 wt
% solution in chlorobenzene. Cu(II) acetate [Cu(OAc)2] and Cu(II)
acetylacetonate [Cu(acac)2] (both from Aldrich) were used as re-
ceived. Bis[N-(2,6-diisopropylphenyl)salicylaldiminate]copper(II)
(III) and bis[5-nitro-N-(tert-butyl)salicylaldiminate]copper(II) (V)
were prepared according to procedures reported in the literature.49-51
New complexes such as bis[3,5-dinitro-N-(2,6-diisopropylphenyl)-
salicylaldiminate]copper(II) (I), bis[3,5-dinitro-N-(phenyl)salicy-
laldiminate]copper(II) (II), and bis[3-nitro-N-(2,6-diisopropylphenyl)-
salicylaldiminate]copper(II) (IV) were prepared as follows.
Synthesis of I. 3,5-Dinitro-N-(2,6-diisopropylphenyl)salicyl-
aldimine (0.881 g, 2.37 mmol) was dissolved in 30 mL of methanol,
and the resulting solution was dropwise added at room temperature
to a solution of 0.181 g (1.00 mmol) of Cu(OAc)2 in 20 mL of
methanol. The reaction mixture was refluxed for 2 h, then it was
allowed to stand overnight at room temperature to precipitate a
green solid, which was filtered, washed with methanol, and vacuum-
dried to give 0.76 g (0.797 mmol) of I (yield 79.7%).
The formation of an ESR-silent Cu(I) active species was
confirmed by the color change of the reaction mixture, which
turned from dark green, typical of copper(II), to dark red on
the progressive addition of MAO-A. This last result supports a
Cu(I)-mediated polymerization mechanism, analogously to what
was recently observed in the case of methyl methacrylate
polymerization by Cu(II) amidinate/MAO catalysts.45 When the
experiment was repeated by using TMA alone, the ESR
spectrum of I completely disappeared at a TMA/Cu molar ratio
equal to 30, but in this case a rapid decomposition to metal
was observed. On the contrary, when TMA-depleted MAO was
used up to an Al/Cu molar ratio equal to 2500, the Cu(II) signal
remained unchanged. These last results confirm that the active
species are formed and stabilized by a synergism between TMA
and the oligomeric MAO, the first component having a reducing
role and the second one a stabilizing effect, as in general
reported for this cocatalyst.46 However, the required very high
excess of MAO-A prevents the isolation and makes very difficult
the spectroscopic characterization of the active species. Work
is in progress on this interesting point, although at least one
residual N,O ligand on the active species should be present,
the performances of I-V being very different from those
observed in the presence of acetate or acetylacetonate precursors.
Conclusions
In this work the catalytic activity of bis(salicylaldiminate)-
copper(II)/MAO catalysts in the vinyl polymerization of nor-
bornene is reported for the first time. The N,O chelate ligand
on the metal center appears necessary for the stability of the
resulting catalytic system. The presence of electron-withdrawing
nitro groups on these precursors enhances the catalytic perfor-
mances. The obtained polymers are characterized by high
molecular weight and a nonstereoregular vinyl-type structure,
typical aspects of a nonradical mechanism. Accordingly, the
ESR study on the copper species formed under polymerization
conditions supports the formation of Cu(I) active species.
Anal. Found:
C 57.43, H 4.91, N 10.78. Calcd for
C38H38N6O10Cu: C 56.89, H 4.77, N 10.47. FT-IR: νCH (aromatic)
3091; νCH (aliphatic) 2966, 2869; νCdN 1622, 1511; νas NO2 1530;
νs NO2 1311; δCH (isopropyl) 1387, 1375 cm-1
.
(47) Vogel, A. I. Text of Practical Organic Chemistry, 5th ed.;
Longman: London, The United Kingdom, 1989.
(48) Pe´deutour, J.-N.; Radhakrishnan, K.; Cramail, H., Deffieux, A. J.
Mol. Catal. A: Chem. 2002, 185, 119.
(45) Shibayama, K. Polym. J. 2003, 35, 711.
(46) Chen, E. Y.-X.; Marks, T. J. Chem. ReV. 2000, 100, 1391, and
references therein.
(49) Yamada, S. Coord. Chem. ReV. 1966, 1, 415.
(50) Yamada, S.; Yamanouchi, K. Bull. Chem. Soc. Jpn. 1982, 55, 1083.
(51) Kalawole, G. A.; Adeyemo, A. O. J. Coord. Chem. 1991, 22, 299.

3664 Organometallics, Vol. 25, No. 15, 2006
Carlini et al.
Synthesis of II. 3,5-Dinitro-N-(phenyl)salicylaldimine (0.656 g,
2.3 mmol) was dissolved in 30 mL of methanol, and the resulting
solution was dropwise added at room temperature to a solution of
0.218 g (1.2 mmol) of Cu(OAc)2 in 20 mL of methanol. The
reaction mixture was refluxed for 2 h, then it was allowed to stand
overnight at room temperature to precipitate a brown solid, which
was filtered, washed with methanol, and vacuum-dried to give 0.48
g (0.79 mmol) of II (yield 66.1%).
Differential scanning calorimetry (DSC) measurements of the
PNB samples were performed on a Mettler TA 4000 instrument
equipped with a DSC 30 flow calorimeter and assisted by TA72
GraphWare software.
Thermogravimetric analysis (TGA) of the PNB samples was
performed on a Mettler TG50 thermobalance and Mettler
TC11 processor, using a dry nitrogen purge and a scan rate of
10 °C/min.
Anal. Found:
C 48.52, H 2.91, N 12.78. Calcd for
X-band ESR spectra of the catalytic systems based on I and the
aluminum cocatalysts in chlorobenzene solution and in the presence
or absence of NB were recorded on a Varian E112 spectrometer
equipped with a Varian E257 unit for temperature control. A Varian
NMR gaussmeter ER 035M and a XL microwave frequence counter
for g measurements were employed. The spectrometer was inter-
faced to an IPC 610/P566C industrial grade Avantech computer
by means of a data acquisition system52 and a software package53
specially designed for ESR experiments.
C26H16N6O10Cu: C 49.10, H 2.54, N 13.21. FT-IR: νCH (aromatic)
3093; νCH (aliphatic) 2967, 2866; cm-1,νCdN 1622; νas NO2 1531;
νs NO2 1313 cm-1
I and II were obtained as amorphous powdery solids. Many
crystallization attempts failed, thus preventing the determination
of their crystal structures.
Synthesis of IV. 3-Nitro-N-(2,6-diisopropylphenyl)salicylaldi-
mine (0.536 g, 1.71 mmol) was dissolved in 30 mL of methanol,
and the resulting solution was dropwise added at room temperature
to a solution of 0.149 g (0.82 mmol) of Cu(OAc)2 in 20 mL of
methanol. The reaction mixture was refluxed for 2 h, then it was
allowed to stand overnight at room temperature to precipitate a
brown solid, which was filtered, washed with methanol, vacuum-
dried, and then recrystallized from methylene chloride/methanol
to give 0.24 g (0.34 mmol) of IV (yield 41%).
X-ray diffractometric analysis was carried out as follows.
A tiny crystal of IV, 0.20 × 0.20 × 0.16 mm wide, sealed in a
Lindeman capillary, was used for the diffractometric sudy. The
measurements were carried out by using a Bruker AXS P4
diffractometer equipped with graphite-monochromated Mo KR
radiation (λ ) 0.71073 Å). The unit cell parameters listed in Table
2 were calculated from the setting angles of 33 strong reflections.
Mp > 300 °C. Anal. Found: C 63.41, H 6.01, N 7.79. Calcd
1
All data were collected in the ω/2θ scan mode, and three standard
reflections were monitored every 97 measurements for checking
crystal decay and equipment stability. Data reduction was done by
the XSCANS program.54 A set of 4297 intensity data were collected
between 1.96° e θ e 26.05° and corrected for Lorentz polarization
and absorption effects (y-scan method). After merging of equivalent
for C38H42N4O6Cu: C 63.90, H 5.93, N 7.84. H NMR analysis
failed due the paramagnetic character of IV. FT-IR: νCH (aromatic)
3093; νCH (aliphatic) 2962, 2875; νCdN 1615; νas NO2 1515; νs NO2
1302; δCH (isopropyl) 1384, 1360 cm-1
.
Polymerization Procedures. NB homopolymerization experi-
ments were carried out in a 50 mL Carius vessel under magnetic
stirring and dry argon atmosphere. In a general procedure the copper
precursor was dissolved in chlorobenzene and then the proper
amount of the solution was transferred into the Carius vessel. Then
NB was added as a 20 wt % solution in chlorobenzene. Finally,
the chosen amount of MAO (MAO-W or MAO-A) was added in
order to reach the proper Al/Cu molar ratio. When the polymeri-
zation experiment was carried out at a temperature > 25 °C, the
Carius vessel was immersed in a thermostatic oil bath at the chosen
temperature. The polymerization was stopped by adding a large
excess of methanol acidified with 5% aqueous HCl to purify the
polymer from catalyst residues. The precipitated polymer was
washed by fresh methanol, then filtered, dried under vacuum,
weighed, and structurally characterized.
Physicochemical Measurements. IR spectra were performed
with a FT-IR Perkin-Elmer Spectrum One spectrophotometer
equipped with an attenuated total reflectance (ATR) apparatus. Data
elaboration was performed by a Spectrum V 3.2 Perkin-Elmer
program. The NMR spectra of PNB samples were performed in
chlorobenzene and 1,1,2,2-d2-tetrachloroethane on a Varian Gemini
200 spectrometer operating at 200 (1H) and 50 (13C) MHz. Size
exclusion chromatography (SEC) measurements were carried out
with a HPLC pump equipped with a 50 µm Rheodyne loop, a
Waters 515 oven at 35 °C, and a Waters 2410 refractive index
detector. A PL 5 µm gel MIXED-C column was used. Chloroben-
zene and 1 mL/min were adopted as the eluent and the elution rate,
respectively. Monodispersed polystyrene samples (Mw ) 1940,
10 050, 96 000, 483 000, 1 730 000, and 3 065 000) were used for
the calibration curve.
2
2
2
reflections (Rint ) [∑|Fo - Fo (mean)|/∑(Fo )] ) 0.1164) 3457
independent reflections were obtained. The poor internal R factor,
11.6%, must be ascribed to the poor quality of the crystal, which
limited to 1461 the intensities greater that 2σ(I).
The structure solution was obtained by standard direct methods
in the C2/c space group. The hydrogen atoms were placed in
calculated positions and in the refinement were let “ride” on the
connected carbon atoms. The final reliability factors (anisotropic
thermal parameters for all heavy atoms) are listed in Table 2.
The calculations were done by using the SHELXTL program55
and some routines contained in the WINGX suite.56
Acknowledgment. The financial support from the Ministero
dell’Istruzione, dell’Universita` e della Ricerca (MIUR) through
the Research Project of National Interest (PRIN) 2004: “New
Strategies for the Control of Reactions: Interactions of Molec-
ular Fragments with Metallic Sites in Unconventional Species”
is gratefully acknowledged.
OM060173I
(52) Ambrosetti, R.; Ricci, D. ReV. Sci. Instrum. 1991, 62, 2281.
(53) Forte, C.; Pinzino, C. EPR-ENDOR; ICQEM-CNR: Rome, Italy,
1992.
(54) XSCANS, X-ray Single-Crystal Analysis System, rel. 2.1; Bruker AXS
Inc.: Madison, WI, 1994.
(55) Sheldrick, G. M. SHELXTL-Plus, rel. 5.03; Bruker AXS Inc.:
Madison, WI, 1995.
(56) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.